Korean characters remain with scrolling.

- [x] I have read through the manual page (`man fzf`)
- [x] I have the latest version of fzf
- [x] I have searched through the existing issues

## Info

- OS
- [ ] Linux
- [ ] Mac OS X
- [x] Windows
- [ ] Etc.
- Shell
- [ ] bash
- [ ] zsh
- [ ] fish
- [x] cmd.exe

## Problem / Steps to reproduce

Browsing directory with file names in Korean(non-Latin?) will leave some ghost chars in the console window as you scroll up/down.

At first, I found this issue in a VIM-embedded terminal. But when I tested in other environments (neovim, detached/embedded FZF windows, GUI/text), result was the same. Korean chars are left always. However I haven't tested it in native Linux terminal.


Also the issue can be easily reproduced with the attached text file.
```type text.txt | fzf.exe```

[test.txt](https://github.com/junegunn/fzf/files/5287713/test.txt)


Reproduce the rendering problem on Windows with cmd.exe using `type text.txt | fzf.exe`, then scroll through the attached text file containing Korean filenames. Compare the console output while scrolling; done means Korean characters no longer remain as ghost characters in the terminal.

Written by the indexing model from the issue text.